Variable Rate Pumping System

ABSTRACT

A pumping system comprising a motor, wherein the motor has an operating speed, a pump coupled to the motor, wherein the pump has a volumetric displacement, a fluid end coupled to the pump, wherein the fluid end is operable to draw fluid from an input and provide fluid to an output, and a control system operable to regulate the motor and the pump in order to provide fluid to the output at a selected pressure and flow rate within a continuous range of pressures and flow rates between the peak horsepower output and peak torque output of the motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/974,437, filed Oct. 27, 2004, and entitled “Variable Rate PumpingSystem,” which is incorporated herein by reference as if reproduced inits entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND

The present invention relates generally to methods and apparatus forsupplying pressurized fluids. More particularly, the present inventionrelates to methods and apparatus for pumping fluids into a wellbore at awide range of pressures and flow rates.

The construction and servicing of subterranean wells often involvespumping fluids into the well for a variety of reasons. For example,fluids may be pumped into a well in conjunction with activitiesincluding fracturing, completion, stimulation, remediation, cementing,workover, and testing operations. A variety of fluids used in theseoperations include fracturing fluids, gels, drilling mud, barite,cement, slurries, acids, and liquid CO₂. In each of these differentapplications, the fluid may be required to be pumped into the well atany point within a wide range of pressures and flow rates.

Pumping units often utilize a power source, such as a diesel or electricmotor, to drive one or more pumps. Many pumping units utilize amultispeed transmission connected between the power source and thepumps. The transmission operates to expand the speed and torque rangeproduced by the power source by providing a set number of gears thattransfer the motion produced by the power source to the pump.

Most multispeed transmissions provide a broad operating envelope ofspeed and torque within which a pump can operate. This operatingenvelope 10 can be illustrated as a relationship between pressure andflow rate as is shown in FIG. 1. Line 15 defines the peak hydraulichorsepower at which the pump can operate and line 16 defines the peaktorque output. Because the transmission comprises a limited set of gearratios 17, the operating envelope 10 of the pump has discrete points 20at which the pump can operate at peak hydraulic horsepower. Thesediscrete points 20, in effect, create gaps 25 where the pump cannotoperate with a given gearing.

Although gaps 25 can be reduced by increasing the numbers of gear ratioswithin a transmission, as the number of gear ratios increases so doesthe complexity and weight of the transmission. Therefore, there areoften practical limits on the number of gear ratios at which atransmission can operate. Thus, there remains a need to develop methodsand apparatus for pumping fluids into a wellbore at wide range ofpressures and flow rates, which overcome some of the foregoingdifficulties while providing more advantageous overall results.

SUMMARY

Disclosed herein is a wellbore pumping system comprising a motor,wherein the motor has an operating speed, a pump coupled to the motor,wherein the pump has a volumetric displacement, a fluid end coupled tothe pump, wherein the fluid end is operable to draw fluid from an inputand provide fluid to an output that is in fluid communication with awellbore, and a control system operable to regulate the motor and thepump in order to provide fluid to the output at a selected pressure andflow rate within a continuous range of pressures and flow rates betweenthe peak horsepower output and peak torque output of the motor.

Further disclosed herein is a method for operating a wellbore pumpingsystem, the method comprising operating a pumping system to providefluid to a wellbore at a selected pressure and flow rate operatingconditions within a continuous range of pressures and flow rates betweenthe peak horsepower and peak torque of the pumping system, monitoringthe pressure and flow rate of the fluid provided by the pumping system,and controlling the pumping system to provide non-discrete variations inthe pressure and flow rate of the fluid provided to the wellbore.Further disclosed herein is a pumping system comprising a motor havingan operating speed, a variable displacement pump coupled to the motor,wherein the positive displacement pump has an operating speed that isrelated to the operating speed of the motor by a fixed ratio, a fluidend coupled to the pump, wherein the fluid end is operable to draw fluidfrom an inlet and provide fluid to an outlet that is in fluidcommunication with a wellbore, and a control system operable to regulatethe operating speed of the motor and the displacement of the pump so asto control the pressure and flow rate of the fluid provided to theoutlet.

Further disclosed herein is a method of operating a wellbore servicingpump comprising controlling the operating parameters of the pump toprovide a fluid output at any combination of pressure and flow ratewithin a range defined by the peak hydraulic horsepower, the peaktorque, the maximum pressure, and the maximum flow rate of the pump,monitoring pressure and flow rate of the fluid output, adjusting atleast one of the operating parameters of the pump to provide a desiredpressure and flow rate of the fluid output.

Thus, the present invention comprises a combination of features andadvantages that enable it to overcome various problems of prior devices.The various characteristics described above, as well as other features,will be readily apparent to those skilled in the art upon reading thefollowing detailed description of the invention, and by referring to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the present invention, reference willnow be made to the accompanying drawings, wherein:

FIG. 1 is a graphical representation of the output characteristics of aprior art pumping system employing a multispeed transmission.

FIG. 2 is a schematic illustration of a pumping system constructed inaccordance with embodiments of the invention.

FIG. 3 is a schematic illustration of a control system for a pumpingsystem constructed in accordance with embodiments of the invention.

FIG. 4 is a graphical representation of the output characteristics of apumping system constructed in accordance with embodiments of theinvention.

FIG. 5 is an isometric view of one embodiment of a pumping systemconstructed in accordance with embodiments of the invention.

FIG. 6 is an isometric view of the displacement controller of FIG. 5.

FIG. 7 is a cross-sectional view of a coupler of the displacementcontroller of FIG. 5.

DETAILED DESCRIPTION

Referring now to an embodiment shown in FIG. 2, pump system 200comprises motor 210, pump 220, fluid end assembly 230, control system240, and displacement control 250. Motor 210 is coupled to pump 220 andprovides power to the pump. Pump 220 works through fluid end assembly230 to pull fluid from inlet 260 to outlet 270. Control system 240monitors the flow conditions (e.g. flow rate and pressure) at outlet 270and regulates motor 210 and pump 220, through displacement control 250,to maintain a desired flow rate and pressure.

Pump 220 is linked to motor 210 without a transmission, such that theirspeeds are related by a fixed ratio. Thus, the speed of pump 220 may bedirectly regulated by controlling the speed of motor 210. Displacementcontrol 250 regulates the displacement (or volume of fluid) that pump220 will move with each revolution or reciprocation. For example,displacement control 250 may act to vary the displacement of pump 220 bychanging the volume of fluid pumped per stroke of a pump cylinder.

One embodiment of control system 240 is shown in FIG. 3. Control system240 comprises servo valve 310, positioner 320, input/output (I/O) device330, processor 340, and power supply 350. Servo valve 310 and positioner320 may be integrated into displacement control 250 of FIG. 2. Servovalve 310 may be an electric, hydraulic, or electro-hydraulic valveproviding control of positioner 320. Positioner 320 may be an electricor hydraulic actuator operable to interface with a displacementdetermining arrangement within pump 220. I/O device 330 monitors theposition of positioner 320 via line 373 and regulates the operation ofservo valve 310 via line 375 in order to control the position of thepositioner. I/O device 330 controls the position of positioner 320 inresponse to flow data 360 received from outlet 270 (see FIG. 2).Processor 340, powered by power supply 350, controls the activity of I/Odevices 330 in response to operator inputs or from a pre-programmedprocedure. I/O devices 330 may comprise two separate devices, one forposition input, and one for servo valve output, such as SDS CAN analoginput and output modules. Processor 340 may be an ACE industrial PC witha board that connects the PC to the I/O devices 330.

Referring now to FIGS. 2 and 3, and by way of example, processor 340receives an instruction to provide a fluid output having a desired flowrate and pressure from fluid end assembly 230. Processor 340 determinesa motor speed and pump displacement that will provide the desired fluidoutput by referencing a predetermined reference table or by calculatingthe appropriate values. Processor 340 transmits the correspondingpredetermined motor speed and pump displacement drive signals for thedesired flow conditions to I/O devices 330. I/O devices 330 sendinstructions to displacement control 250 via line 375 and motor 210 vialine 370. Displacement control 250 establishes the displacement for pump220 by setting positioner 320 using servo valve 310. Speed controlcommands 370 are issued to motor 210 from I/O device 330 of controlsystem 240.

As pump 220 operates, I/O device 330 receives flow data 360 from outlet270 and adjusts motor 210 and displacement control 250 to maintain thedesired flow characteristics. The motor speed and displacement can beoptimized for horsepower, torque, fuel efficiency, or a combination ofthose factors. For example, if maximum horsepower is selected, theengine speed (and thus pump speed) and pump displacement would be chosento give the best rate for maximum engine horsepower to be developed.Thus, maximum horsepower would be transferred to the pump and to thefluid being pumped. Similar choices could be made for optimalefficiency, or for optimal torque. In each case, the engine speed anddisplacement would be chosen to allow for the optimum parameter value tobe developed by the engine and transferred to the pump with much lowerloss than with a transmission. So, for example, if optimum efficiency ischosen, the engine speed and the pump stroke (displacement) would bechosen to allow the engine to operate at optimum efficiency, saving fueland reducing emissions. The efficiency would be greater not only becauseof operating the engine at its optimal speed for the load but would alsobe greater than with a transmission because losses from thetransmission, which lower efficiency, would be avoided.

A continuous feedback control loop also allows for adjusting to changingfluid conditions, including compressibility and inlet flow rate, andprovides a quick-to-neutral capability. The quick-to-neutral capabilityoffers a significant advantage should a pumping shutdown be needed. Whenactivated, a relief valve would quickly release the hydraulic pressurethat was holding the current pump displacement and fluid back pressurewould rapidly stroke the positioner back to the zero rate pumpingposition. This could be done much more quickly than stopping the engineor pump from rotating, because to stop them, their inertia must beovercome. This ability could be further enhanced by incorporating aspring in the displacement actuator so that when pumping against lowpressure, the spring would assist in more rapidly returning the pump tothe zero pumping rate position.

By controlling the speed of motor 210 and the displacement of pump 220,any desired pressure and flow rate combination within a given operatingenvelope can be provided at outlet 270. Referring now to FIG. 4, anoperating envelope 400 for pump system 200 can be illustrated as arelationship between pressure and flow rate. Because there are nodistinct gear ratios, as are shown in FIG. 1, operating envelope 400includes all pressure and flow rate combinations within the operationallimits of peak hydraulic horsepower 410, peak torque output 415, maximumoperating pressure 420, maximum flow rate 430, and minimum flow rate440. Therefore, pump system 200 can operate within a continuous range ofpressure and flowrate combinations between peak hydraulic horsepower 410and peak torque output 415. When compared to the prior art multispeedtransmission operating envelope of FIG. 1, the operating envelope ofFIG. 4 has no gaps between peak hydraulic horsepower 410 and peak torqueoutput 415 where there are pressure and flow rate combinations where thesystem cannot operate.

Eliminating the multispeed transmission also eliminates a complex pieceof machinery, reducing capital and maintenance costs as well as reducingthe weight of the overall system. Many pumping systems are portablesystems that are mounted on skids, trailers, or chassis, so weight andsize of components is an important issue. For example, to be easilytransported by road, the size of a portable component of a system islimited to a width of approximately eight feet and a height ofapproximately thirteen feet. With the weight of the multispeedtransmission eliminated, a higher horsepower or capacity system could beused in applications that were previously limited by the weight and/orsize of the components.

Embodiments of pumping system 200 may utilize any combination of motors,variable displacement pumps, and fluid end assemblies as may be desired.For example, an electric or diesel motor may be used to provide power tothe pump. The pump may be any variable displacement pump providingeasily adjusted variable displacement and capable of the horsepower andpressure requirements needed for the desired application. For example,pumps may be used having mechanisms as described in U.S. Pat. No.6,742,441, entitled “Continuously Variable Displacement Pump withPredefined Unswept Volume,” or U.S. Pat. No. 6,976,831 filed Jun. 25,2003, entitled “Transmissionless Variable Output Pumping Unit,” or U.S.Pat. No. 7,409,901 filed Oct. 27, 2004, entitled “Variable StrokeAssembly,” all of which are incorporated herein by reference in theirentirety for all purposes.

Referring now to FIG. 5, one embodiment of a pump system 500 is shownincluding displacement controller 510, speed reducer 520, variabledisplacement pump 530, and fluid end 540. Pump system 500 is powered byan electric motor or diesel engine (not shown) through drive lineconnection 550. Variable displacement pump 530 comprises a “Sandersonmechanism” as is shown and described in U.S. Pat. No. 6,019,073,entitled “Double Ended Piston Engine,” and U.S. Pat. No. 6,397,794,entitled “Piston Engine Assembly,” and U.S. Pat. No. 6,446,587, entitled“Piston Engine Assembly,” all of which are incorporated herein byreference in their entirety for all purposes.

Variable displacement pump 530 includes a rotating shaft, the positionof which can be linearly adjusted to control the displacement of thepump. The shaft is rotated by the motor turning drive line connection550, which is coupled to the shaft through speed reducer 520. Speedreducer 520 transfers rotation from drive line connection 550 to theshaft at a fixed ratio as established by one or more gears disposedwithin the speed reducer. Thus, the rotational rate of pump 530 isdirectly proportional to the rotational rate at which the motor isoperated.

The displacement of pump 530 is controlled by axially displacing therotating shaft that is coupled to the motor. The displacement of therotating shaft can be controlled by a variety of devices includinghydraulic cylinders, jack-screws, ball-screws, pneumatic cylinders, andelectric actuators. These devices preferably provide adjustment of therotating shaft in both directions along its axis. Referring back to FIG.3, these control devices act as positioner 320 that is controlled byservo 310.

As shown in FIG. 6, displacement controller 510 controls the lineardisplacement of the rotating shaft 602. Displacement controller 510includes coupler 604 that interfaces between shaft 602 and hydraulicpiston 606. Hydraulic piston 606 is connected to the power end of pump530 by tie rods 608. Coupler 604 supports rotational movement of shaft602 and allows hydraulic piston 606 to apply an axial force to moveshaft 602 and thus adjust the stroke of pump 530.

Referring now to FIG. 7, coupler 604 includes housing 610, bearings 612,rotating retainer 614, and connecting screw 616. Housing 610 is mountedto pump 530 and includes flange 618. The extending shaft of hydraulicpiston 606, see FIG. 6, engages flange 618 to apply linear force tohousing 610. Shaft 602, see FIG. 6, is attached to screw 616, which isconnected to rotating retainer 614 and allowed to rotate relative tohousing 610 by bearing 612. Therefore, shaft 602 can freely rotate aboutits longitudinal axis as it is moved along that axis by piston 606.

Referring back to FIG. 5, as the reciprocating speed of the pistons ofpump 530 are driven by the motor through speed reducer 520, the strokeof those pistons is controlled by displacement controller 510. Thus, bycontrolling the speed at which the pump reciprocates and thedisplacement of each stroke of the pump pistons, the output pressure andflow rate can be regulated.

Fluid end 540 is coupled to the pistons of pump 530 such that fluid isdrawn in through suction inlet 560 and expelled through fluid outlet570. Fluid end 540 may comprise check valve assemblies 580 thatinterface with the pistons of pump 530, where each check valve 580 is influid communication with both inlet 560 and outlet 570. The check valveassemblies 580 allow fluid to be drawn only from the low pressure inlet560 and high pressure fluid output only through outlet 570.

By eliminating the need for a heavy-duty, multi-speed transmission, thevariable displacement pumping system provides a smaller package for agiven pump rating. The table below lists various examples of pumpingsystems operating at 275 revolutions per minute.

Plunger Max Max dia. Stroke Number Max Rate Rod load Pressure HHP inchinch Cyl bpm lbf psi 800 4.5 8 3 10.8 180000 11300 1000 4 10 3 10.7180000 14300 2000 4.5 12 5 27.0 250000 15700 3000 5 12 3 20.0 30000015300

The smaller package allows higher capacity pumping systems to be mountedon chassis, trailers, or skids comparably sized to smaller pumpingsystems. The variable displacement pumping system also provides a morecomplete operating envelope as compared to conventional transmissionsystems.

While exemplary embodiments of this invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the scope or teaching of this invention. Theembodiments described herein are exemplary only and are not limiting.Many variations and modifications of the system and apparatus arepossible and are within the scope of the invention. For example, therelative dimensions of various parts, the materials from which thevarious parts are made, and other parameters can be varied, so long asthe apparatus retain the advantages discussed herein. Accordingly, thescope of protection is not limited to the embodiments described herein,but is only limited by the claims that follow, the scope of which shallinclude all equivalents of the subject matter of the claims.

1. A method comprising: operating a pumping system to provide a fluid ata pressure and a flow rate within a continuous range of pressures andflow rates between a peak horsepower and a peak torque of the pumpingsystem; monitoring the pressure and the flow rate of the fluid providedby the pumping system; controlling the pumping system to providenon-discrete variations in the pressure and the flow rate of the fluid;and pumping the fluid into a subterranean wellbore.
 2. The method ofclaim 1, wherein the pumping system does not comprise a transmission. 3.The method of claim 2, wherein the pumping system comprises a pump and amotor, wherein changes in the pressure and the flow rate are controlledby varying a speed of a motor.
 4. The method of claim 3, wherein astroke of the pump is varied by axial translation of a rotating pumpshaft.
 5. The method of claim 2, wherein the pumping system comprises apump and a motor, and wherein the pressure and the flow rate arecontrolled by varying a displacement of the pump.
 6. The method of claim5, wherein a ratio of a rotational speed of the motor to a rotationalspeed of the pump is fixed.
 7. The method of claim 5, wherein thedisplacement of the pump can be adjusted by varying a stroke of thepump.
 8. A method comprising: controlling a plurality of operatingparameters of a pump to provide a fluid output at any combination ofpressure and flow rate within a range defined by a peak hydraulichorsepower, a peak torque, a maximum pressure, and a maximum flow rateof the pump; monitoring the pressure and the flow rate of the fluidoutput; and adjusting at least one of the operating parameters of thepump to provide a desired pressure and flow rate of the fluid output,wherein the fluid is a wellbore servicing fluid.
 9. The method of claim8, wherein the pump is not coupled to a transmission.
 10. The method ofclaim 8, wherein the adjusted operating parameter comprises a speed ofthe pump.
 11. The method of claim 10, wherein the speed of the pump isadjusted by adjusting the speed of a motor operating the pump.
 12. Themethod of claim 11, wherein the speed of the pump is related to thespeed of the motor by a fixed ratio.
 13. The method of claim 8, whereinthe adjusted operating parameter comprises a displacement of the pump.14. The method of claim 13, wherein the displacement of the pump isdetermined by the axial position of a rotating shaft.
 15. The method ofclaim 14, wherein the axial position of the rotating shaft is regulatedby a displacement controller comprising a coupling engaged with therotating shaft and a hydraulic cylinder operable to engage the couplingso as to axially translate the rotating shaft.
 16. A method comprising:operating a pumping system comprising a pump and a motor to provide afluid at a pressure and a flow rate within a continuous range ofpressures and flow rates between a peak horsepower and a peak torque ofthe pumping system, wherein the pumping system does not comprise atransmission; and pumping the fluid into a subterranean wellbore. 17.The method of claim 16, wherein the pressure and the flow rate aredetermined by operating parameters consisting essentially of: adisplacement of the pump and a speed of the motor.
 18. The method ofclaim 17, wherein the displacement of the pump is determined by theaxial position of a rotating shaft.
 19. The method of claim 18, whereinthe axial position of the rotating shaft is regulated by a displacementcontroller comprising a coupling engaged with the rotating shaft and ahydraulic cylinder operable to engage the coupling so as to axiallytranslate the rotating shaft.
 20. The method of claim 16, wherein thefluid comprises fracturing fluid, drilling mud, barite, cement, liquidCO₂, or combinations thereof.